1. Field of the Invention
Embodiments of the present invention relate to a thermometer code generator and devices employing such a thermometer code generator. More particularly, embodiments of the present invention relate to a simple and/or highly reliable thermometer code generator and devices, e.g., highly reliable frequency-locked loop (FLL) employing such a thermometer code generator.
2. Description of the Related Art
A clock data recovery (CDR) circuit generally employs a clock that has a locked frequency in order to recover a data exactly. A frequency-locked loop (FLL) may include a voltage controlled oscillator (VCO). The FLL may generate a signal that is synchronized to a target frequency, and may output a lock detection signal when a frequency of the signal is locked.
A conventional FLL may employ both fine and course tuning, and may include an up/down counter and decoder. The counter may count a number of up times and a number of down times related to tuning a VCO clock, and the decoder may convert a binary code representing the counted number to a thermometer code. Employing such a decoder may increase time delay, increase complexity of the decoder when a bit number of the counter increases and/or increase an error of the thermometer code when the decoder becomes complicated. As a result of such error in the generated thermometer code, the VCO clock generated by the VCO may not be locked. Also, as current that flows through the VCO may be changed by a first control voltage for fine tuning and a second control voltage for coarse tuning, a duty ratio of the VCO clock may not be 50%.